Flame retardant compositions

ABSTRACT

A silicone elastomer stock that exhibits improved flame resistance in the cured state consisting essentially of a silicone elastomer, a filter, and a small amount of a flame retardant material selected from the group consisting of platinum and platinum-containing materials.

This is a continuation, of application Ser. No. 129,323 filed Mar. 11,1980 .Iaddend..[.This application.]. .Iadd.which .Iaddend.is acontinuation of application Ser. No. 463,898 filed June 14, 1965.

This invention relates to organopolysiloxane compositions havingimproved flame-retardant properties. More particularly, this inventionis concerned with a composition of matter which, in the cured state,exhibits improved flame-retardant properties and which comprises, (1) anorganopolysiloxane convertible to the cured, solid, elastic state andconsisting essentially of silicon atoms, oxygen atoms, and organicgroups selected from the class consisting of methyl radicals, aromaticradicals selected from the class consisting of aryl and halogenated arylradicals, and vinyl radicals, from 0 to 35 mol percent of the organicgroups being silicon-bonded aryl or halogenated aryl radicals and from 0to 2% of the organic groups being silicon-bonded vinyl radicals, therebeing from 1.98 to 2.05 organic groups per silicon atom, (2) a finelydivided inorganic filler, and (3) a material containing platinum.

Cured, solid, elastic organopolysiloxane, hereinafter referred to as"silicone rubbers," whether vulcanized by means of heat in the presenceof organic peroxides or other organic curing agents, or when vulcanizedwith high energy electrons are known to have good heat resistance atelevated temperatures, such as 150°-250° C., and even higher. However,in certain applications, particularly in wire coating, it has been foundthat these silicone rubbers do not have the desired flame retardancy.

Although I do not wish to be bound by theory, it is probable that theorganic groups in the organopolysiloxane structure continue to burnunless extinguished by external means, even when the silicone rubber isfilled with an inorganic filler, such as finely divided forms of silicondioxide. When flame retardancy is an important requirement, as in moldedor extruded parts, these silicone rubbers cannot be utilized even thoughthey are completely adequate for many other uses.

A method for improving the flame retardancy of a silicone rubber isshown in U.S. Pat. 2,891,033--Savage, where a finely divided cupreousmaterial is combined with other components of a silicone rubber toimpart flame retardancy. However, while this additive does improve theflame retardancy of most silicone rubbers and is entirely adequate forsome uses, the combination of the polymer with the copper compoundresults in an extremely dark colored composition which makes it verydifficult to provide a wide range of colors, as is often necessary withsilicone rubber, for example in color-coding of multi-conductor cables.The dark color can be masked to a degree, but the agents which areemployed for such masking, for example, titanium dioxide, do not fullyhide the dark color and, additionally, detract to a degree from theflame retardancy. The same problem of coloration is present, to adegree, in the composition described in U.S. Pat. 3,154,515--Berridge,where copper, copper oxides, or copper halides are utilized as a flameretardant additive for organopolysiloxane compositions which areconvertible to the cured, solid, elastic state at room temperature.

In accordance with the present invention, it has unexpectedly beendiscovered that by incorporating a small amount of a platinum-containingmaterial in a filled silicone rubber composition containing nosilicon-bonded hydrogen, the burning time and percentage of thecomposition which is consumed are markedly reduced. Theplatinum-containing materials which are employed are, in general, thosewhich are well known to the art as catalysts for the addition of thehydrogen of an SiH group across the unsaturated bond of an Si-olefinmaterial.

The organopolysiloxane which is convertible to the cured, solid, elasticstate can be any of the organopolysiloxane gums known in the art whichfall within the composition range stated above and have a viscosity offrom about 5,000,000 to 50,000,000 centistokes. Theseorganopolysiloxanes are advantageously obtained by condensing adiorganodihydrolyzable silane, for example, dimethyldichlorosilane, withor without small amounts of monoorganotrihydrolyzable silanes ortriorganomonohydrolyzable silanes, for example, methyltrichlorosilane,trimethylchlorosilane, etc., and thereafter effecting condensation ofthe hydrolysis product using a condensing agent, for instance, analkaline condensing agent, such as potassium hydroxide, sodiumhydroxide, etc., or an acidic condensing agent, such as ferric chloride,etc. Alternately, cyclic polymers of dimethylsiloxane can be condensedwith an alkaline condensing agent to give the desired organopolysiloxanewhich is convertible to the cured, solid, elastic state. Whatever themethod of formation of the convertible organopolysiloxane, the finalmaterial can contain up to 35 mol percent of phenyl radicals bonded bysilicon-carbon links and up to 2% of vinyl radicals bonded throughsilicon-carbon links. Thus, when the convertible material is formed byhydrolysis, a portion of the starting material can bediphenyldihydrolyzable silane, methylphenyldihydrolyzable silane,methylvinyldihydrolyzable silane, divinyldihydrolyzable silane, etc., orthe monoorganothrihydrolyzable or triorganomonohydrolyzable silanescontaining these radicals.

It is essential to the production of truly flame retardant compositionsthat a quantity of a filler be present. In general any filler systemwhich is residually non-alkaline, i.e., acidic or neutral, can beemployed. Any of the finely divided silica fillers, generally used forsilicone rubber, such as, silica aerogel, fumed silica, ground quartz,and finely divided silica treated with organosilicon materials, e.g.,trimethylchlorosilane, etc., can be employed. The treatment of silicafillers with organosilicon materials are as described, e.g., in U.S.Pats. 2,938,009--Lucas and 3,004,859--Lichtenwalner. The amount offiller present can vary within wide ranges, from 10 to 300 parts offiller per 100 parts of the organopolysiloxane gum. Preferably, thefiller is present in an amount of from 40 to 125 parts per 100 parts ofthe organopolysiloxane gum. Up to about 2/3 of the total silica fillercan be replaced by such materials as carbon black, titanium dioxide, ordiatomaceous earth, or a combination of these materials, so long as aresidual alkalinity in the filler system does not result. However, whileclay has often been employed as a filler for silicone rubber, it hasunexpectedly been found that convertible organopolysiloxane materialsfilled with alkaline clay, alone, do not exhibit the flame retardancyshown by the materials filled with a finely divided silica or a mixtureof silica with one or more of the other materials mentioned previously.

The platinum-containing material which is used is, as previouslymentioned, any of the materials generally utilized in SiH--Si-olefinreactions. Among the forms of this platinum are elemental platinum, asshown in U.S. Pat. 2,970,150--Bailey and platinum-on-charcoal,platinum-on-gamma-alumina, platinum-on-silica gel, platinum-on-asbestos,and chloroplatinic acid

    (H.sub.2 PtCl.sub.6.6H.sub.2 O)

as mentioned in Pat. 2,823,218--Speier. Further, the platinum-containingmaterial can be selected from those having the formula (PtCl₂.olefin)₂and H(PtCl₃.olefin), as described in U.S. Pat. 3,159,601--Ashby. Theolfin shown in the previous two formulas can be almost any type ofolefin, but is preferably an alkene having from 2 to 8 carbon atoms, acycloalkylene having from 5 to 7 carbon atoms, or styrene. Specificolefins utilizable in the above formulas are ethylene, propylene, thevarious isomers of butylene, octylene, cyclopentene, cyclohexene,cycloheptene, etc. A further platinum-containing material usable in thecomposition of the present invention is the platinum chloridecyclopropane complex (PtCl₂.C₃ H₆)₂ described in U.S. Pat.3,159,662--Ashby.

Still further, the platinum-containing material can be a complex formedfrom chloroplatinic acid with up to two mols per gram-atom of platinumof a member selected from the class consisting of alcohols having theformula ROH, ethers having the formula ROR', aldehydes having theformula RCHO and mixtures of the above as described and claimed in thecopending application of Harry F. Lamoreaux, Ser. No. 207,076, filedJuly 2, 1962, and assigned to the same assignee as the presentinvention. The substituent R in the above formulas is a member selectedfrom the class consisting of alkyl radicals having at least 4 carbonatoms, alkyl radicals substituted with an aromatic hydrocarbon radical,and alkyl radicals substituted with an OR' group, where R' is a memberselected from the class consisting of monovalent hydrocarbon radicalsfree of aliphatic unsaturation and monovalent radicals free of aliphaticunsaturation and consisting of carbon, hydrogen, and oxygen atoms, witheach oxygen atom being attached to two atoms, at least one of which is acarbon atom and up to one of which is a hydrogen atom.

Small, but effective, amounts of the platinum-containing material aresufficient to impart the desired flame retardancy to the siliconerubber. In general, amounts of from 3 to 250 parts per million, asplatinum, based on the organopolysiloxane gum, can be used. Preferably,the amount is from 25 to 100 p.p.m., as platinum, based on theorganopolysiloxane gum. The platinum-containing material can be employedin amounts greater than 250 parts per million, but, due to the cost ofthe materials, utilization of greater than 250 parts per million is notpreferred as the increased amounts do not provide significantimprovement in the flame retardancy of the final material.

It is particularly surprising that the platinum-containing materialsshould be found, in conjunction with a non-alkaline filler system, toprovide flame retardancy in a silicone rubber. Very often, other noblemetal-containing compositions have been considered equivalent toplatinum in promoting the addition of the hydrogen atom of the SiH groupacross the unsaturated bond of an Si-olefin group. Included among thesenoble metals are ruthenium, rhodium, iridium, palladium, and osmium.That the effect of the platinum in the present invention is not of thesame catalytic type is demonstrated by the fact that others of thegenerally equivalent noble metals do not provide the desired flameretardancy. For example, a palladium-on-charcoal catalyst containing 10%palladium was incorporated into a polydimethylsiloxane gum containing0.2% vinyl radicals, and 41.5 parts of fumed silica and 65 parts ofground quartz, per 100 parts of the organopolysiloxane, and thecomposition was cured with 1% of benzoyl peroxide for 1 hour at 300° F.In the flame test, 100% of the composition was consumed whether thepalladium content was 40 parts per million or 100 parts per million.

While the previously described organopolysiloxane gum, silica filler orcombination of silica filler with others of the enumerated fillers, andplatinum-containing material are essential to the production of aflame-retardant silicone rubber composition, other materials can beadded without impairing this flame retardant property. Some of theseadditional materials may even enhance the flame retardancy. Among theadditional materials which can be added are rubber process aids, such asalkoxy-containing, hydrocarbon-substituted polysiloxane fluids asdescribed in U.S. Pat. 2,954,357--Fekete and hydroxylated silanes asdescribed in U.S. Pat. 2,890,188--Konkle et al. Additionally, resinousorganopolysiloxane materials such as those formed from tetrafunctionalalkylsilicates, triorganomonofunctional silanes, and, in some cases,difunctional diorganosilanes, as disclosed and claimed in U.S. Pat.2,857,356--Goodwin, Jr., can also be employed.

The order of addition of the various components to the composition isimmaterial. All can be added simultaneously, or the filler,platinum-containing material, and additional materials, when they arepresent, can be added at varying times to the organopolysiloxane gum anda homogeneous blend obtained. Following blending of the variousmaterials, the material is cured using any of various curing agents as,for example, benzoyl peroxide, tertiary butyl perbenzoate,bis-(2,4-dichlorobenzoyl) peroxide, etc. These curing agents can bepresent in varying amounts ranging from about 0.3% to as high as 6 to10%, by weight, or more, based on the weight of the organopolysiloxanegum. Further, the convertible organopolysiloxane gum can be cured by anyother method known in the art without adversely affecting the flameretardant properties imparted by the filler and platinum-containingmaterial. Cure is accomplished with the various peroxide and perbenzoatecatalysts by heating with slight pressure at from about 100° to 200° C.for times ranging from 5 to 15 minutes. In addition to, or instead ofthis press cure, the silicone rubber composition can be treated attemperatures of from about 200° to 500° C. for sufficient time to assurecomplete conversion of the polysiloxane gum to a substantially infusibleand insoluble state.

The process of the present invention will now be more fully illustrated.These illustrations should not be considered as limiting in any way thefull scope of the present invention as covered in the appended claims.

In order to evaluate the flame retardant properties of the siliconerubber compositions described in the examples, a test was employed whichconsisted of suspending a cured strip of the silicone rubber, havingdimensions of 0.5 in. by 6 in. by 0.075 in. from a metal wire in a glasschimney in a draft-free atmosphere over a blue flame (approximately1100° C.) in such a manner that the tip of this strip is suspended 1 in.into the flame. The strip is held in the flame for a period of 20seconds, at which time the flame is removed and the time required forcomplete extinguishment of the flame is measured. The time is recordedas the "burning time," in seconds. The test strip is then freed of looseash and weighed to determine the "percent consumed" by the fire. Amaterial which burned for less than 140 seconds and was no more than 50%consumed was considered sufficiently flame retardant.

EXAMPLES 1-5

A series of runs were made to show the effectiveness of thefiller-platinum system with a polydimethylsiloxane gum. Each formulationincluded 100 parts of a polydimethylsiloxane gum having an approximateaverage viscosity of 7,500,000 centistokes, and 40 parts of a silicaaerogel. Each of the formulations was press cured using, as a catalyst,about 2.2 parts of a composition containing about 50% benzoyl peroxidein a polydimethylsiloxane fluid having a viscosity at 25° C. of 1300centistokes. The platinum was incorporated using a methanol solution ofchloroplatinic acid. Table I shows the parts per million of platinumbased on the polydimethylsiloxane gum, the burning time, and the percentconsumed in the flame retardancy test.

                  TABLE I                                                         ______________________________________                                                           Burning Time                                               Example Pt, p.p.m. (seconds)  Percent consumed                                ______________________________________                                        1        0         187        100                                             2       5.3        115        50                                              3       27         107        50                                              4       53         105        50                                              5       121         94        50                                              ______________________________________                                    

Thus, it can easily be seen that the incorporation of the minimumquantity of silica filler with between 5 and 121 parts per million ofplatinum, based on the polysiloxane gum, significantly reduces theburning time of a material which is otherwise completely consumed byflame and, further, reduces the percent consumed by the flame to only 50percent.

EXAMPLES 6-7

These examples illustrate the effect of a filler which is slightlyalkaline on the flame retardancy of a silicone rubber which includesplatinum, as otherwise disclosed in this invention. Theorganopolysiloxane gum was the same as that employed in Examples 1through 5 in an amount of 100 parts. The filler, in this case, wasdiatomaceous earth composed of almost 90% silica, but additionallycontaining between 5 and 10% of potassium oxide, iron oxide, andaluminum oxide. Each composition was cured for 24 hours at 480° F. with5 parts of a composition containing 50% of benzoyl peroxide in apolydimethylsiloxane fluid having a viscosity at 25° C. of 1300centistokes. Without platinum, the composition described above burnedfor approximately 130 seconds and was entirely consumed in the flame.The platinum was obtained by dissolving 1 mole of H₂ PtCl₆ ·6H₂ O in 7moles of octyl alcohol. This platinum-alcohol solution was maintained ata temperature of 70°-80° C. and a pressure of approximately 15 to 20 mm.for 60 hours while the ratio of chlorine to platinum was reduced to 2atoms of chlorine per atom of platinum. The water and hydrogen chloridewhich resulted were removed by holding the temperature at 70°-80° C. Theresulting product will hereinafter be referred to as the organicplatinum complex. Addition of about 68 p.p.m. as platinum, based on theorganopolysiloxane gum, reduced the burning time of the compositiondescribed above to 90 seconds and the percent consumed to 67%, asignificant reduction, but beyond the range which would be consideredacceptable.

EXAMPLES 8-9

The effectiveness of a composition of the present invention in retardingflame was demonstrated in these examples employing 100 parts of apolydimethylsiloxane gum having an approximate viscosity of 7,500,000centistokes where 0.2% of the silicon-bonded methyl groups were replacedwith silicon-bonded vinyl groups. In addition, each compositioncontained 43 parts of a fumed silica treated with about 16% ofoctamethylcyclotetrasiloxane in accordance with the aforementioned Lucaspatent. Example 8, which contained no platinum-containing material, was100% consumed in the flame retardancy test. Example 9 had the sameformulation as Example 8 except that it contained 133 p.p.m. ofplatinum, derived from the organic platinum complex, based on theorganopolysiloxane gum. This material was press cured. It burned for 102seconds and was 30-35% consumed in the flame retardancy test.

EXAMPLES 10-17

The organopolysiloxane gum employed in Examples 8 and 9 was also used inthese examples in an amount of 100 parts. However, in each case, inaddition to 43 parts of octamethylcyclotetrasiloxane-treated fumedsilica and 100 parts of gum, each composition contained ground quartz.The platinum in Example 16 was added as the organic platinum complex,while in each of the other examples the platinum was derived from a 10%methanol solution of chloroplatinic acid hexahydrate. Table II, inaddition to showing the data of Table I, shows the parts of groundquartz. In each case the material was cured with 1.1 parts of acomposition containing 50% dichlorobenzoyl peroxide in apolydimethylsiloxane fluid having a viscosity of 1300 centistokes at 25°C.

                  TABLE II                                                        ______________________________________                                             Parts                       Burning                                                                              Percent                                    ground                      time   con-                                  Ex.  quartz  Pt, p.p.m.                                                                             Cure       (sec.) sumed                                 ______________________________________                                        10   65       0       1 hr. at 300° F.                                                                  150    100                                   11   65      78       Press      60     15                                                          1 hr. at 300° F.                                                                  45     10                                                          24 hrs. at 480° F.                                                                25     10                                                          96 hrs. at 480° F.                                                                15      5                                    12   65       8       Press      72     25                                    13   65      40       "          62     10                                    14   65      80       "          66     15                                    15   65      181      "          65     10                                    16   122     245      "          60     10                                                          20 min. at 300° F.                                                                95     15-20                                 ______________________________________                                    

As can be seen from the examples above, the inclusion of the groundquartz does not adversely affect the flame retardancy of the siliconerubber with the platinum-containing material, when the filler andplatinum are in the correct amounts. Additionally, mixtures ofnon-alkaline fillers have no adverse affect upon the ultimate flameretardancy.

EXAMPLES 17-20

These examples illustrate the substitution of a portion of the silicafiller with a carbon black having a pH of about 7 . This filler systemprovided flame retardancy essentially equivalent to the non-alkalinesilica fillers, alone. Each composition contained 100 parts of apolydimethylsiloxane gum wherein 0.35% of the silicon-bonded methylgroups were replaced by silicon-bonded vinyl groups. Additionally, eachcomposition contained 17 parts of untreated fumed silico and 30 parts ofcarbon black. Each of the formulations was press cured with 0.9 part ofdicumyl peroxide. The platinum in each example was obtained from a 10%methanol solution of chloroplatinic acid hexahydrate. The results of theflame retardancy test for each of these examples, along with the p.p.m.of platinum contained in each of the formulations, based on theorganopolysiloxane gum, are shown in Table III.

                  TABLE III                                                       ______________________________________                                                             Burning time                                                                             Percent                                       Example  Pt, p.p.m.  (sec.)     consumed                                      ______________________________________                                        17       0           180        100                                           18       5.7         132        50                                            19       29           88        35                                            20       57           73        30                                            ______________________________________                                    

Thus, it can be seen that flame retardancy is achieved when a portion ofthe non-alkaline silica filler is replaced by other fillers where theoverall filler system has no residual alkalinity.

EXAMPLES 21-23

These examples demonstrate the ability to incorporate significantamounts of other polysiloxane materials into the silicone rubbercomposition, without impairing the flame retardancy of the finalmaterial. In each of these examples the composition contained 100 partsof the polydimethylsiloxane gum having about 0.2% of the silicon-bondedmethyl groups replaced with silicon-bonded vinyl groups, previouslydescribed. Additionally, each contained 43 parts of theoctamethylcyclotetrasiloxane treated fumed silica and a quantity of theresin described as Sample 1 of Example 1 of the aforementioned Goodwin,Jr., Pat. 2,857,356 (hereinafter referred to as MQD). Example 23 alsocontained 75 parts of ground quartz. In each case the material was curedfor one hour at 300° F. using 1.5 parts of the dichlorobenzoylperoxide-polydimethylsiloxane composition and the platinum was added inthe form of the organic platinum complex. Table IV shows the amount ofplatinum, based on the organopolysiloxane gum, the amount of MQD, andthe performance in the flame retardancy test.

                  TABLE IV                                                        ______________________________________                                                 MQD                Burning                                                                              Percent                                    Example  (Parts) Pt, p.p.m. time   Consumed                                   ______________________________________                                        21       4.8     0          215    80-85                                      22       5.5     3          75     20                                         23       5.5     3          65     25                                         ______________________________________                                    

As can be seen from these examples, while the addition of a MQD materialhas little effect upon the flame retardancy of the silicone rubber, itsinclusion has no adverse effect upon the rubber when theplatinum-containing material is added.

EXAMPLES 24-25

Silicone rubber compositions comprising polymers having silicon-bondedphenyl groups are known to inherently possess a degree of flameretardancy. However, even the flame retardancy of these materials can beimproved by incorporating a platinum-containing material into the rubbersystem. Two silicone rubber compositions were prepared with 100 parts oforganopolysiloxane gum, 42 parts of fumed silica, 10.5 parts ofdiatomaceous earth, and 2 parts of titania. The polysiloxane gum was amethylphenylpolysiloxane having an approximate viscosity of 25,000,000centistokes where the phenyl substituents constituted 5% of the totalmethyl and phenyl substituents. The compostion of each example was curedfor one hour at 300° F. employing 4 parts of the previously describeddichlorobenzoyl peroxide-polydimethylsiloxane blend. The platinum wasadded in the form of the organic platinum complex. In the flameretardancy test, the cured composition without platinum continued toburn for 85 seconds and was 35% consumed. However, the same composition,with 68 p.p.m. platinum, based on the organopolysiloxane gum, burned for60 seconds and was only 5% consumed.

EXAMPLES 26-27

The performance of a composition containingmethylphenylvinylpolysiloxane gum, filler, and platinum-containingmaterial in accordance with the present invention is demonstrated bythese examples. The organopolysiloxane was a gum having an approximateviscosity of 25,000,000 where about 5% of the silicon-bonded organicgroups were phenyl and about 0.2% were vinyl, the remainder beingmethyl. Two compositions were formulated with 100 parts of the gum, 46parts of octamethylcyclotetrasiloxane-treated fumed silica, and 14 partsof untreated fumed silica. Each of the compositions was cured for 1 hr.at 300° F. in the presence of about one part of the dichlorobenzoylperoxidepolydimethylsiloxane material. The platinum was again added asthe organic platinum complex. When tested in the flame retardancy testthe material without platinum burned for 66 seconds and was 30%consumed, while the same material with 69 p.p.m. platinum, based on theorganopolysiloxane gum, burned for 54 seconds and was less than 5%consumed.

EXAMPLE 28

A further indication of the need for a neutral or acidic filler isdemonstrated in this example. A series of samples were preparedcontaining 100 parts of a polydimethylsiloxane gum having an approximateviscosity of 7,500,000 centistokes, 10 parts of a silica aerogel, and120 parts of Whitetex clay. Four of the compositions were treated with a10% solution of chloroplatinic acid hexahydrate in methanol to yieldplatinum contents of from 8 to 181 parts per million, based on thepolysiloxane gum. In the flame retardancy test the press curedcomposition without platinum was 100% consumed and burned for 117seconds. However, each of the other compositions was also 100% consumed,the only apparent affect of the platinum being to reduce the burningtime from 115 seconds in the case of a content of 8 p.p.m. platinum,gradually to 68 seconds in the case of the material with 181 p.p.m.platinum.

With the exception of rubbers containing such coloring fillers as carbonblack, each of the flame retardant silicone rubbers formulated accordingto the present invention is easily colored. Thus, a wide range ofcolored flame-retardant silicone rubbers is possible. The uses to whichthese materials can be put are generally the same as those recited inPat. 2,891,033--Savage. Thus, they can be employed for electricalconductor insulation, gaskets, heater ducts, wrap-around tapes forelements which may be subjected to elevated temperatures, etc.

What we claim as new and desire to secure by Letters Patent of theUnited States is: .[.
 1. A composition of matter which in a cured stateexhibits improved flame-retardant properties, the compositioncomprising:(1) 100 parts of an organopolysiloxane gum convertible to thecured, solid, elastic state and consisting essentially of silicon atoms,oxygen atoms, and organic groups selected from the class consisting ofmethyl radicals, aromatic radicals selected from the class consisting ofaryl and halogenated aryl radicals in an amount of from 0 to 35 molpercent of the organic groups, and from 0 to 2 mol percent of the totalorganic groups of vinyl radicals, there being from 1.98 to 2.05 organicgroups per silicon atom, (2) a finely divided, non-alkaline inorganicfiller in an amount of from 10 to 300 parts, by weight, and (3) small,but effective amount to impart flame retardancy of a platinum containingmaterial not exceeding 250 parts per million, by weight based on theorganopolysiloxane gum..]. .[.2. The cured product of claim 1..]. .[.3.The composition of claim 1 wherein the inorganic filler is present in anamount of from 40 to 125 parts..]. .[.4. The composition of claim 1wherein the platinum-containing material is present in a range toprovide from 3 to 250 parts per million, by weight based on theorganopolysiloxane gum, of platinum..].
 5. .[.The.]. .Iadd.A.Iaddend.composition of .[.claim 4 wherein.]. .Iadd.matter which in acured state exhibits improved flame-retardant properties, thecomposition comprising: (1) 100 parts of an organopolysiloxane gumconvertible to the cured, solid, elastic state and consistingessentially of silicon atoms, oxygen atoms, and organic groups selectedfrom the class consisting of methyl radicals, aromatic radicals selectedfrom the class consisting of aryl and halogenated aryl radicals in anamount of from 0 to 35 mol percent of the organic groups, and from 0 to2 mol percent of the total organic groups of vinyl radicals, there beingfrom 1.98 to 2.05 organic groups per silicon atom, (2) a finely divided,non-alkaline inorganic filler in an amount of from 10 to 300 parts, byweight, and (3) small, but effective amount to impart flame retardancyof a platinum containing material, said platinum-containing materialbeing present in a range to provide .Iaddend.from 25 to 100 parts permillion.Iadd., by weight .Iaddend.of platinum .[.are provided..]..Iadd.,based on the organopolysiloxane gum. .Iaddend. .[.6. The composition ofclaim 1 wherein the inorganic filler is a silica aerogel..]. .[.7. Thecomposition of claim 1 wherein the inorganic filler is a fumedsilica..]. .[.8. The composition of claim 1 wherein the filler is afumed silica treated with an organopolysiloxane..]. .[.9. Thecomposition of claim 1 wherein the inorganic filler in a mixture of afumed silica and ground quartz..]. .[.10. The composition of claim 1wherein the filler is a mixture of fumed silica and carbon black..]..[.11. The composition of claim 1 wherein the inorganic filler is amixture of fumed silica, diatomaceous earth, and titanium dioxide..]..Iadd.12. A composition of matter which in a cured state exhibitsimproved flame-retardant properties, the composition comprising: (1) 100parts of an organopolysiloxane gum convertible to the cured, solid,elastic state and consisting essentially of silicon atoms, oxygen atoms,and organic groups selected from the class consisting of methylradicals, aromatic radicals selected from the class consisting of aryland halogenated aryl radicals in an amount of from 0 to 35 mol percentof the organic groups, and from 0 to 2 mol percent of the total organicgroups of vinyl radicals, there being from 1.98 to 2.05 organic groupsper silicon atoms, (2) a finely divided, non-alkaline inorganic fillerin an amount of from 10 to 300 parts, by weight, (3) a peroxide curingagent, and (4) small, but effective amount to impart flame retardancy ofa platinum containing material not exceeding 250 parts per million, byweight based on the organopolysiloxane gum. .Iaddend..Iadd.13. The curedproduct of claim
 12. .Iaddend. .Iadd.14. The composition of claim 12wherein the inorganic filler is present in an amount of from 40 to 125parts. .Iaddend. .Iadd.15. The composition of claim 12 wherein theplatinum-containing material is present in a range to provide from 3 to250 parts per million, by weight based on the organopolysiloxane gum, ofplatinum. .Iaddend. .Iadd.16. The composition of claim 15 wherein from25 to 100 parts per million of platinum are provided. .Iaddend..Iadd.17. The composition of claim 12 wherein the inorganic filler is asilica aerogel. .Iaddend. .Iadd.18. The composition of claim 12 whereinthe inorganic filler is a fumed silica. .Iaddend. .Iadd.19. Thecomposition of claim 12 wherein the filler is a fumed silica treatedwith an organopolysiloxane. .Iaddend. .Iadd.20. The composition of claim12 wherein the filler is a mixture of a fumed silica and ground quartz..Iaddend. .Iadd.21. The composition of claim 12 wherein the filler is amixture of fumed silica and carbon black. .Iaddend. .Iadd.22. Thecomposition of claim 12 wherein the inorganic filler is a mixture offumed silica, diatomaceous earth, and titanium dioxide. .Iaddend..Iadd.23. A composition of matter which in a cured state exhibitsimproved flame-retardant properties, the composition comprising: (1) 100parts of an organopolysiloxane gum convertible to the cured, solid,elastic state and consisting essentially of silicon atoms, oxygen atoms,and organic groups selected from the class consisting of methyl radicalsand aromatic radicals selected from the class consisting of aryl andhalogenated aryl radicals in an amount of from 0 to 35 mol percent ofthe organic groups, There being from 1.98 to 2.05 organic groups persilicon atom, (2) a finely divided, non-alkaline inorganic filler in anamount of from 10 to 300 parts, by weight, and (3) small, but effectiveamount to impart flame retardancy of a platinum containing material, notexceeding 250 parts per million, by weight based on theorganopolysiloxane gum. .Iaddend. .Iadd.24. The composition of claim 23which further includes a peroxide curing agent. .Iaddend. .Iadd.25. Thecured product of claim
 23. .Iaddend. .Iadd.26. The composition of claim23 wherein the inorganic filler is present in an amount of from 40 to125 parts. .Iaddend. .Iadd.27. The composition of claim 23 wherein theplatinum-containing material is present in a range to provide from 3 to250 parts per million, by weight based on the organopolysiloxane gum, ofplatinum. .Iaddend. .Iadd.28. The composition of claim 27 wherein from25 to 100 parts per million of platinum are provided. .Iaddend..Iadd.29. The composition of claim 23 wherein the inorganic filler is asilica aerogel. .Iaddend. .Iadd.30. The composition of claim 23 whereinthe inorganic filler is a fumed silica. .Iaddend. .Iadd.31. Thecomposition of claim 23 wherein the filler is a fumed silica treatedwith an organopolysiloxane. .Iaddend. .Iadd.32. The composition of claim23 wherein the inorganic filler is a mixture of a fumed silica andground quartz. .Iaddend. .Iadd.33. The composition of claim 23 whereinthe filler is a mixture of fumed silica and carbon black. .Iaddend..Iadd.34. The composition of claim 23 wherein the inorganic filler is amixture of fumed silica, diatomaceous earth, and titanium dioxide..Iaddend. .Iadd. A composition of matter which in a cured state exhibitsimproved flame-retardant properties, the composition comprising: (1) 100parts of an organopolysiloxane gum convertible to the cured, solid,elastic state and consisting essentially of silicon atoms, oxygen atoms,and organic groups selected from the class consisting of methylradicals, aromatic radicals selected from the class consisting of aryland halogenated aryl radicals in an amount of from 0 to 35 mol percentof the organic groups, and from 0 to 2 mol percent of the total organicgroups of vinyl radicals, there being from 1.98 to 2.05 organic groupsper silicon atom, (2) a finely divided, non-alkaline inorganic filler inan amount of from 10 to 300 parts, by weight, and (3) small, buteffective amount to impart flame retardancy of a platinum containingmaterial, said platinum-containing material being present in a range toprovide from 25 to 250 parts per million of platinum by weight, based onthe organopolysiloxane gum. .Iaddend. .Iadd.36. The cured product ofclaim
 35. .Iaddend. .Iadd.37. The composition of claim 35 wherein theinorganic filler is present in an amount of from 40 to 125 parts..Iaddend. .Iadd.38. The cured product of claim
 37. .Iaddend. .Iadd.39.The composition of claim 37 wherein the filler is a mixture of fumedsilica and carbon black. .Iaddend. .Iadd.40. The cured product of claim39. .Iaddend. .Iadd.41. The composition of claim 37 wherein theinorganic filler is a mixture of fumed silica, diatomaceous earth, andtitanium dioxide. .Iaddend. .Iadd.42. The cured product of claim 41..Iaddend. .Iadd.43. A composition of matter which in a cured stateexhibits improved flame-retardant properties, the composition being freefrom silicon-bonded hydrogen and comprising: (1) 100 parts of anorganopolysiloxane gum convertible to the cured, solid elastic state andconsisting essentially of silicon atoms, oxygen atoms, and organicgroups selected from the class consisting of methyl radicals, aromaticradicals selected from the class consisting of aryl and halogenated arylradicals in an amount of from 0 to 35 mol percent of the organic groups,and from 0 to 2 mol percent of the total organic groups of vinylradicals, there being from 1.98 to 2.05 organic groups per silicon atom,(2) a finely divided, nonalkaline inorganic filler in an amount of from10 to 300 parts, by weight, and (3) small, but effective amount toimpart flame retardancy of a platinum containing material not exceeding250 parts per million, by weight based on the organopolysiloxane gum..Iaddend. .Iadd.44. The composition of claim 43 which further includes aperoxide curing agent. .Iaddend.